Age resisting nonstaining rubber composition and method of producing same



Patented July 28, 1953 AGE RESISTIN G NONSTAINING RUBBER COMPOSITION AND METHOD OF PRO- DUCIN G SAME Joseph Ambelang, Akron, Ohio, assignor to The Firestone Tire & Rubber Company, Akron, Ohio, a corporation of Ohio No Drawing. Application July 1, 1950, Serial No. 171,761

Claims.

This invention relates to vulcanized, as well as unvulcanized but vulcanizable, rubber compositions resistant to deterioration normally attending aging of the compositions, whether by the action of heat, light, oxygen, ozone or any combination thereof. The invention includes the production of the improved rubber compositions by incorporating a new and improved class of non-staining antioxidants or stabilizers into a rubbery composition prior to vulcanization thereof. This application is a continuation-in-part of my copending application Serial No. 641,007, filed January 12, 1946, now abandoned.

The new antioxidants are prepared by reacting 3 to 4 moles of an aliphatic aldehyde with 6 moles of a dialkylphenol hvaing the following formula:

in which R is an alkyl radical containing 3 to 10, inclusive, carbon atoms.

The aldehydes which are used in preparing the new antioxidants are formaldehyde, acetaldehyde, crotonaldehyde, butyraldehyde, isobutyraldehyde, propionaldehyde, valeraldehyde, isovaleraldehyde, 2-ethyl-butyraldehyde, and. similar low molecular weight aliphatic aldehydes.

The mono-alkyl m-cresols used in preparing the antioxidants oi the invention are the 2-alkyl- 5-methylphenols in which the alkyl radical is propyl, isoprppyl, n-butyl, isobutyl, tart-butyl, the various isomeric amyl radicals, the various isomeric hexyl radicals, the various isomeric heptyl radicals, the various isomeric octyl radicals, the various isomeric nonyl radicals and the various isomeric decyl radicals. In lieu of the alkyl radicals enumerated, substituted alkyl radicals, such as cyclohexyl, benzyl, a-methylbenzyl, a,u.-dimethylbenzyl, various nuclearly alkylated benzyl radicals, and homologs of the cyclohexyl radical are within the scope of the invention.

The dialkylphenol-aldehyde reaction appears to be a condensation reaction, and it may be accelerated by use of an acid or an alkali catalyst. It is important, however, to avoid using any substantial excess of the aldehyde over the proportion thereof set out above, in order to produce relatively low molecular weight reaction products and to avoid producing the high molecular weight condensates, as the latter are relatively poor antioxidants.

The following examples are illustrative of the preparation of the antioxidants of the invention.

EXALEPLE 1 Two moles (328 grams) of 2-tert-b methylphenol with 0.45 mole (59.4 grar r g if paraldehyde (equivalent to 1.35 moles acetaldehyde) and ml. of hydrochloric acid (sp. gr. 1.19) were stirred under reflux on a steam bath for 4 hours. The reaction mixture was neutralized with sodium carbonate and the product taken up in a benzene-a1coho1 mixture. After removal of solvent, a crystalline reaction product remained, weighing 84% of the weight of the oialkylphenol. After recrystallization from benzene the reaction product melted at 201-202 C.

The acetaldehyde butyl m cresol reaction product, so prepared, was tested as an antioxidant 1n the following tire white sidewall stock formula:

Parts by Ingredients Weight ass The test stock wasmixed and vulcanized 60 minutes at 280 F., and then compared with a blanlr stock (identical with the test stock but cgntamini 21o antioxidant) vulcanized under the s me con i ions. The com arative d out in Table 1. p altar are set TABLE 1 Cured 60 min. at 280 F. Blank west 7 Stock Stock Nor%alhlllropertiesz l o us at 400% elongation .s.i Tensile Strength at break (p. i.) ::I n g Elongation at break (percent) n 640 640 Propertles After Aging 2 Days in Oven at 212 Fl Modulus at 400% elongation (p. s. i.) 1 000 1 225 Tensile Strength at break (p. s. i.) 2' 250 2' 515 Elongation at break (percent) 540 550 Retentlon of Tens1le Strength (percent) 63 71 Oxygen Absorption Test Hours to absorb 5 ml of oxygen .L 15 58 1 I. R. Shelton an hW' my, vol. 38, that? 1biifftifitfgfioiiiritif Table 1 shows that the antioxidant of Example 1 substantially protects natural rubber from oxidation and the effects of heat. The protection against absorption of oxygen gas is very pronounced. Also, it was observed that the antioxidant did not stain the white rubber stock in which it was tested, the test stock being as free from discoloration as the blank stock containin no antioxidant.

EXAMPLE2 To a solution of 22 grams (0.1 mole) ofZ-tertoctyl-5-methylphenol in 60 ml. of glacial acetic acid there was added a solution of grams of concentrated sulfuric acid in 40 m1. of glacial acetic acid. Formalin (4.2 ml.--0.056 mole-HCHO) was added to the mixture, and then an additional 100 ml. of glacial acetic acid was added to produce a clear solution. The reaction mixture was allowed to stand 24 hours at room temperature, and then it was diluted with an equal volume of water. The resulting mixture was extracted with a mixture of petroleum ether and ether, the ether extract was thoroughly washed with water, and the extract was then dried' over anhydrouspotassium carbonate. The dried extract was filtered and evaporated to leave'the dialkyl-phenol-formaldehyde reaction product as alight brown gum weighing" 23 grams. The reaction product,upon testing in the manner of Example 1,-is found to be a superior non-discoloring antioxidant for rubber.

EXAMPLE 3 A mixture of 2 moles (328 grams) of 2-tert- 'but'yl-5 methylphenol, 1 mole grams) of formaldehyde (as a aqueous solution) and 0.2 mole ofs'odium hydroxide (as a 10% aqueous 1 solution) was stirred for 15 hours at room temperature. The reaction mixture Was then neutrallzed with aceticacid, and the neutralized mix- 'ture was extracted with benzene. The benzene product, prepared as in Example 3 ,'was tested as a stabilizer 'or oxidation inhibitor for synthetic rubber by incorporating 2% by weight of the reaction product/based upon the synthetic rubber, 'into an unsta-bilized latex of GR-S- (emulsion polymers of a 1,3-butadiene and emulsion 'copolymers of a 1,3-butadiene with styrene 'ora substituted' styrene, the'cop'olymers containing-at least c'ombinedbutadiene or homolog thereoi all of which polymers have been and are being pro-. .duced in. United StatesGovernment-owned synthetic rubber plants). The resulting latex-was coagulated in knownmanner to produce a synthetic rubber coagulum containing thestabilizer of the invention uniformly distributed therethrough. The coagulum Was dried in an oven for 20 hours at 75 'C., and its physical condition and color were noted. Then the dried 'coagul'um was aged in an oven at 110 C. oneday and any changes in physical condition and color noted. The antioxidant orstabilizer-of the invention was compared to a commercial, secondaryaromatic amine-type of antioxidant by -carrying out the same steps of coagulating a GR-'-S latex containing 2% of the amine-type antioxidant, drying the coaguium, oven aging same, and notingphysical properties as -above. "Also; unstabil-ized" GR-S latex was carried through the same procedure to provide data on a blank'? control. The data or v observations are set out'i-n Table 2.

TABLE 2 Stabilizer tests in GR-S The data in Table 2 show that the antioxidants of the invention are non-discoloring stabilizers or inhibitors for synthetic rubber of the GR-S type,

' even superior to a well-known commercial antioxidant of the amine-type.

The antioxidants of the invention are likewise effective as stabilizers or oxidation inhibitors for other vulcanizable synthetic rubbers produced by polymerizing or copolymerizing a 1,3-butadiene (including hydrocarbon homologs of butadiene) and/or a vinyl monomer other than a styrene, for example, acrylonitrile, methacrylonitrile, an ester of vinyl alcohol, an ester of acrylic or methacrylic acids, vinylpyridine, vinylcarbazole' or other low molecular weight vinyl monomers. The antioxidants are of commercial value in the synthetic rubber known as GPc-A (which is the United States Government designation of a rubbery copolymer of acrylonitrile and 1,3-butadiene, containing at least 50% of combined butadiene) The antioxidant of Example 3 was also evaluated in a white GPt-S vulcanizate of the following formula:

White GR-S stock The reaction product of Example 3 was incorporated in the GPv-S latex and the mixture was coagulated to provide the stabilized GR-S. The white stock prepared in accordance with the above formula was vulcanized by heating 30, 50 and 70 minutes at 300 F. The physical properties of the three cures of the vulcanizate were entirely equal to the properties of a control stock in which the amine-type antioxidant previously mentioned was substituted for the reaction product of Example 3. After both stocks wereaged for 4 days in an oven at 0., properties of all cures of both stocks were still equal.

The two white GR-S stocks (the 50 minute cure of each) were then exposed to natural outdoor weathering (direct sunlight) in Akron, Ohio, for one month, side by side. The observations made upon the two stocks are set out in Table 3.

TABLE 3 Natural weathering of white GR-S vulcanizates After One Month Antioxidant Dor Color Checking Dialkylphenol aldehyde No change No change. None.

product of Example 3. Amine-type antioxidant.-- Dark cream. Light tan. Slight.

be obtained by vulcanizing with sulfur with or without an accelerator, vulcanizing without free sulfur but in the presence of any of the wellknown sulfur-donors such as the phenol polysulfides and homologs thereof, the dithiocarbamates, as Well as cross-linking agents such as dithiols, nitroand nitroso-compounds, as are well known in the rubber art for vulcanizing a rubber. Any rubber, natural or synthetic capable of being vulcanized by any of the foregoing vulcanizing agents is contemplated.

What is claimed is:

1. A rubber composition resistant to deterioration, comprising vulcanized rubber containing a relatively small amount of the reaction product of 3 to 4 moles of formaldehyde and 6 moles of a dialkylphenol of the formula wherein R is a hydrocarbon radical containing 3 to 10 carbon atoms.

2. Method of making a rubber product resistant to deterioration, comprising vulcanizing rubber in the presence of a relatively small amount of the reaction product of 3 to 4 moles of acetaldehyde and 6 moles of a dialkylphenol of the formula wherein R is a hydrocarbon radical containing 3 to 10 carbon atoms.

3. Vulcanized rubber containing a relatively small amount of the reaction product of 3 to 4 moles of formaldehyde and 6 moles of 2-tertbutyl-5-methylphenol.

4. Vulcanized rubber containing a relatively small amount of the reaction product of 3 to 4 moles of formaldehyde and 6 moles of 2-tertoctyl-5-methylphenol.

5. Vulcanized rubber containing a relatively small amount of the reaction product of 3 to 4 moles of acetaldehyde and 6 moles of 2-tertbutyl-5-methylphenol.

6. vulcanizable rubber containing a, relatively small amount of the reaction product of 3 to 4 moles of formaldehyde and 6 moles of 2-tertbutyl-5-methylphenol.

7. vulcanizable rubber containing a relatively small amount of the reaction product of 3 to 4 moles of formaldehyde and 6 moles of 2-tertoctyl-5-methylphenol.

8. Vulcanizable rubber containing a relatively small amount of the reaction product of 3 to 4 moles of acetaldehyde and 6 moles of 2-tertbutyl-5-methylphenol.

9. vulcanizable rubber containing a relatively small amount of the reaction product of 3 to 4 moles of an aliphatic aldehyde and 6 moles of a dialkylphenol of the formula HaC HaC

wherein R is a hydrocarbon radical containing 3 to 10 carbon atoms.

JOSEPH C. AMBELANG.

References Cited in the file of this patent FOREIGN PATENTS Country Date Great Britain May 10, 1949 Number 

1. A RUBBER COMPOSITION RESISTANT TO DETERIORATION, COMPRISING VULCANIZED RUBBER CONTAINING A RELATIVELY SMALL AMOUNT OF THE REACTION PRODUCT OF 3 TO 4 MOLES OF FORMALDEHYDE AND 6 MOLES OF A DIALKYLPHENOL OF THE FORMULA 